A valuable asset to the irrigation industry has been the development of irrigation systems that travel while sprinkling large land areas with water and require virtually no personnel attention during operation. Substantial elimination of the labor costs that were earlier required has greatly enhanced the commercial success of large field irrigation. Although many different types of irrigation systems have been developed over the years, the type of irrigation system that is most prevalent is the circular irrigation system which incorporates a plurality of sprinkler pipe sections that are each supported by a mechanism for inducing movement to the pipe sections. In circular irrigation systems a central pivot tower is provided that also serves as a water supply and one extremity of the irrigation system is connected thereto causing the entire irrigation system to revolve about the pivot during continuous irrigation operations. Although circular irrigation systems have been quite successful, it is clear that greater crop yields and lower cost irrigation would be achieved if the irrigation system were capable of irrigating rectangular land areas or other specifically shaped land areas as opposed to circular areas. One attempt to accomplish more rectangular irrigation through the use of circular irrigation systems is through the use of corner irrigation spray devices that are activated only during four small segments of each revolution of the irrigation system. Although the increase of land area irrigation through the use of irrigation guns is not insubstantial, it would nevertheless be commercially desirable to provide an irrigation system that was capable of irrigating the entirety of a large rectangular land area.
In the past, irrigation systems have been developed for irrigation of rectangular fields, but in order to provide for proper operation of the irrigation system, it is generally deemed necessary that a plurality of tracks or guideways be provided in order to physically guide the irrigation system over the land area. Of the number of patented devices that have been developed with track or guideway control in mind, U.S. Pat. No. 3,608,827, to Kinkead is typically representative. Linearly movable irrigation systems have also been developed that do not necessitate the use of tracks or guideways such as taught by U.S. Pat. No. 3,613,703, to Stout which utilizes a guide rail 52 for reference during movement over a land area and traverses by alternate movement and pivoting of each of the ends of the system. In the case of the structure identified in the patent to Stout the ambulatory irrigation system is so arranged and controlled that each end of the composite line alternately can be caused to travel a predetermined distance along an arcuate path with the opposite end of the composite line temporarily being substantially at the center of curvature of the arcuate path and with the entire line thus swinging forwardly in alternate angular direction as it moves over the land area. More simply, one extremity of the irrigation system remains static and serves as a pivot during a portion of the movement and the sequence is then reversed causing the other extremity to remain static while the first extremity is caused to move. The ends of the system are not capable of simultaneous movement.
It is considered desirable to provide a linearly movable irrigation system that does not require a track or guideway to control movement thereof such as is the case with Kinkead U.S. Pat. No. 3,608,827 and which does not cause excessive water distribution on certain of the land section such as is likely to occur when each end of the irrigation system alternately moves forward.
U.S. Pat. No. 3,707,164 to Clemons and U.S. Pat. No. 3,974,845 to Indresaeter disclose linearly movable irrigation systems which do not require a track or fixed guideway for control of the system movement. Clemons teaches a method and apparatus for maintaining an irrigation system within predetermined distance from an elongated reference line. In one embodiment, Clemons selectively energizes adjacent tractors to provide a steering action relative to the guide and in another embodiment the tractor wheels are also turned simultaneously to move the irrigation system toward or away from the reference guide. Clemons also teaches maintaining the alignment between adjacent tractors by varying the flow of hydraulic fluid to hydraulic motors on the tractors for speed control. It should be noted that the steering control systems taught by Clemons employ control and power systems at substantially each mobile support unit. Further, the control systems of Clemons are actuated by only a single type of input so that the system response is corrective of only the particular input selected.
U.S. Pat. No. 3,974,845 to Indresaeter teaches an irrigation system which is controlled by stopping and starting mover units located at extremities of the system. As described therein, the control system is provided with inputs functionally related to the linear displacement from the guide reference of the mover unit adjacent the guide reference and to the angular alignment of the irrigation system with respect to the guide reference. The correction of either linear or angular misalignment is accomplished by causing the entire irrigation system to pivot about one extremity or the other to maintain the system within preselected limits. Lateral displacement can be corrected only by a substantial number of correcting manuevers. Further, there is no input signal related to the stresses being developed in the irrigation pipe spans in order to preclude corrective action which could result in excessive system stresses.
Accordingly, it is a primary feature of the present invention to provide a novel linearly movable irrigation system that moves in substantially linear manner over a land area and is capable of irrigating the entirety of a generally rectangular land area or irrigating a land area of an irregular shape.
It is also a feature of the present invention to provide a novel linearly movable irrigation system whereby control of the movement of the system is accomplished by a first control system steering a mover unit adjacent an elongated reference and an independent second control system maintaining the relative rotation of the irrigation pipe spans relative to the steerable mover unit.
It is an even further feature of the present invention to provide a novel linearly movable irrigation system that moves in linear manner over a land area and, in the event of the occurrence of predetermined misalignment of the irrigation system relative to the reference, the irrigation system is automatically self-steering to maintain its travel within a defined boundary.
It is yet another feature of the present invention to provide a novel linearly movable irrigation system employing sensing devices for determining angular alignment of the irrigation pipe spans with respect to a pivot located on the steerable mover unit and for determining the stresses in the irrigation pipe spans and controlling the angular alignment and stress by movement relative to the steerable mover unit.
It is also an object of the present invention to provide a novel linearly movable powered mover unit adjacent a reference such as an elongated guide surface which may be straight or curved as desired, wherein the powered mover unit is provided with a control mechanism that senses linear displacement of the mover unit relative to the reference for steerably controlling travel of the mover unit relative to the elongated reference.
It is another object of the present invention to provide a novel linearly movable irrigation system in which angular alignment and stresses in the irrigation pipe spans are controlled by movement relative to a powered mover unit and independent from a fixed guide reference.
It is also a feature of the present invention to provide a novel linearly movable irrigation system wherein a plurality of individually supported and driven sections are incorporated into an elongated irrigation system and wherein movement of each of the sections is controlled by its angular relationship with an adjacent irrigation section, such angular relationship control overridden under certain circumstances by control signals received from a power and control portion of the irrigation system.